A Study in Mischief
by BookkeeperThe
Summary: Living with Sherlock Holmes, John has grown somewhat accustomed to sudden, unexpected insanity. This, however, is a bit much, even for him.
1. Chapter 1

**Notes: Takes place at some vaguely Avenger-y time, and sometime after Hounds of Baskerville. Brief, vague references to Doctor Who. Massive credit to my friend Holly (sleipnirlokison on tumblr) for coming up with the premise and betaing. This was meant to be crack, but then Loki happened and I accidentally angsted all over everything. It gets more fluffy after the first chapter, though. Tell me what you think!**

John was slightly alarmed when Sherlock caught his arm halfway up the stairs, halting his progress towards their flat. He was less alarmed by the 'caught his arm' bit, and more by the 'halfway up the stairs' one. Usually, if something was amiss, the consulting detective could tell before they were even out of the cab, let alone through the door.

Sherlock was silent, his eyes narrowed, listening hard. John pricked his own ears. Seeping through the door was an entirely unfamiliar voice, low and threatening.

". . . any idea who I am?"

"Yes, yes," replied Mrs. Hudson breezily, and John winced, feeling Sherlock go rigid beside him. He prayed that whoever was in there wasn't foolish enough to lay a finger on her, for her sake and for that of the unknown intruder. "You're one of Sherlock's clients. Don't worry; he gets all sorts. Eat your biscuits, dear."

Sherlock removed his hand from John's arm and began to creep – no, to prowl up the stairs. John followed him while Mrs. Hudson continued to fuss over the intruder.

"Honestly, the state of you! Worse than Sherlock. Though he hasn't been so bad these days, what with that doctor of his looking after him . . ."

"Yes, thank you, Mrs. Hudson," said Sherlock firmly as he pushed the door open.

A man was sitting in Sherlock's customary chair, clad in an expensive black suit and green scarf despite the warm weather. Mrs. Hudson hadn't been exaggerating when she said that he was worse than Sherlock. His skin was sallow and pale, contrasting sharply with his dark, greasy hair. Even through his layers of fabric it was obvious that he was unhealthily thin; best guess, John would say that he was naturally slim to begin with and made slimmer by neglect and stress. The circles under his eyes attested to that.

He had been frowning at a Jammy Dodger when they entered, but swept to his feet with effortless poise an instant later. His eyes nearly matched Sherlock's in color and definitely matched them in intensity.

"Sherlock Holmes," the stranger greeted. He did not extend his hand. "I have heard such . . . fascinating stories about you."

"I rather suspect I've heard some about you, as well," Sherlock returned. John wondered absently how two people who were approximately the same height could _both_ look down their noses at each other. "Loki."

The stranger smiled a shark's smile as the air around him began to shimmer. John gaped in disbelief and Mrs. Hudson gave a startled squeak as the man's outfit shifted before their eyes. Wait – had Sherlock said _Loki_?

"You are certainly more clever than most humans," the man – god? No, no, absolutely not – said. His attire had solidified into some cross between a medieval tunic and a leather jacket, all black and gold and green. "Unless, of course, you simply recognize my face from your elder brother's pilfered records . . ."

"I have better things to do with my time than to steal from my brother," said Sherlock.

Despite the situation, John found he still had enough of his composure intact to roll his eyes at this blatant falsehood.

"It's not exactly a difficult deduction," Sherlock continued. "Your earlier question to Mrs. Hudson suggests that you have a very high opinion of your own status; I'd say delusions of grandeur, but your manner speaks of a sort of breeding which is difficult to fake. Not just nobility, but royalty. Not delusions, then, but not entirely accurate, either."

"Sherlock," said John warningly, seeing the cold imitation of mirth slip from the – the god's face. Sherlock ignored him.

"You're clearly unwell; underfed and overstressed. The extent of your malnutrition is beyond mere absentmindedness; it is almost certainly the result of starvation, self-inflicted or otherwise. Your body language speaks of psychological trauma which could only be produced by repeated physical abuse over an extended period of time."

"Sherlock," said John, more sharply. Loki was trembling slightly, eyes wide, and – oh god, were those tears? Yes. He was crying. Sherlock was making a Norse god cry. Of course he was. Christ.

"That sort of treatment would never have been allowed if you still belonged to the class which you ascribe to yourself; exiled, then. Any exiled royalty on Earth I'd know about it, so obviously you are of extraterrestrial origin. You're too defensive for a king, which makes you a prince, which means that some older member of your family must still be alive, and yet you can't or won't go to them for help. Additionally, you were startled and confused by Mrs. Hudson's care, as if you're not accustomed to anyone looking towards your wellbeing. You aren't just estranged from your family; you were an outcast from the very beginning.

"Conclusion: you are an exiled alien prince with a vested interest in Earth, despised by your people and rejected by your family –"

"_Sherlock_!"

Sherlock finally closed his mouth, looking at John with some mixture of bemusement and offense.

"What?"

That was when the ball of blue light hit him.


	2. Chapter 2

"We have a bit of a situation."

Mycroft's voice was utterly unsurprised in John's ear.

"_Yes, I was informed of some rather . . . unusual occurrences in your area. Would you care to explain?" _

"Sherlock's been turned into a ferret."

There was a long pause.

"_. . . I beg your pardon?"_

John sighed, watching the sleek black animal dart around and under and into the couch. The god had disappeared without a trace and John had sent a rather panicky Mrs. Hudson for a lie down and an herbal soother, leaving him to keep track of a Sherlock who was suddenly even more slippery than usual.

"Your brother, Sherlock Holmes, has been transformed into a ferret. By an angry Norse god. Either that or he's slipped something into my drink. If he has, I'm going to kill him. I might just kill him anyway," he added, reaching forward to pull his shoes out of the creature's reach. It hissed at him.

"_Ah,"_ said Mycroft, as if that cleared everything up. _"Would the god in question happen to be dark haired, somewhat sickly, and more than somewhat emotionally unstable?"_

"That's him. Sherlock called him Loki."

"_Yes, I expect he did. There is a car outside your flat. Bring the ferret."_

The line went dead.

As it turned out, getting ferret-Sherlock to go someplace it didn't want to go was nearly as difficult as getting human-Sherlock to do the same. Mycroft's people were no help whatsoever, though, to their credit, their expressions did not so much as twitch as John struggled to keep hold of the squirming animal. Once inside it retreated to the far end of the seat and glared at him with an eerily familiar expression of resentment. He was nearly certain that no normal ferret had ice-blue eyes.

"This is so ridiculous," he muttered to himself.

The skirmish was repeated when it came time to exit the car, but John eventually managed to wrap the ferret in his jacket. It protested vehemently at this indignity.

"Oh, shut up," he told it. "This is your own fault, you know."

"As difficult as ever, I see."

John did not jump at Mycroft's voice, which echoed dramatically in the empty building. He also refused to be even remotely impressed when the elder Holmes brother stepped out from behind one of the numerous bookcases, his umbrella swinging at his side.

"A library?" John questioned instead. "You couldn't have picked a place where he's _more_ likely to get lost if he runs off? Because I was really looking forward to spending my entire evening chasing after a stroppy rodent."

Mycroft smiled thinly.

"Ferrets are not rodents," he said. He reached towards the not-rodent, only to pull back with a yelp. It was the most undignified sound John had ever heard from him, and the cause was made clear by his bloodied finger.

"He bites," John said unnecessarily while Mycroft wrapped what was undoubtedly a very expensive handkerchief around the wound.

Mycroft gave him a sour look, but did not dignify the statement with a verbal response.

"You have some way to put him back to normal, right?" John asked. "Some secret government shape-shifting machine or something?"

"There are certain . . . options I may pursue."

"Tut, tut."

This time John _did_ jump, spinning towards the voice and automatically tightening his grip on the bundle in his arms. Loki prowled towards them from the shadows, his eyes and his armor glinting.

"Such _lies_, Mr. Holmes. You may as well tell him the truth now. What good does it do to delay the inevitable?"

The god came to a halt between them, his lips curling into a malicious smirk.

"Your defenses are in tatters, your institutions disbanded and your champion dead. You have neither the technology to reverse the transformation nor the ability to contact those who can. You have no power I fear and no gift I desire. You have _nothing_, Mycroft Holmes."

Mycroft met Loki's icy smile with one of his own, and John could have sworn that the physical temperature of the room dropped by several degrees.

"You seem very certain of your information, Loki Laufeyson."

Something about that sentence was apparently a terrible insult, because Loki stiffened, the smile sliding off his face.

"Your bluster will achieve nothing, little man. Your brother is lost to you."

And just like that, he was gone.

"Well, that was pleasant," John commented to the empty air, firmly ignoring the chill in his bones. "He's wrong, of course." He turned to face the elder Holmes, who was frowning at the space which Loki had just occupied. "Mycroft? He is wrong, isn't he?"

"Hm? Oh, yes, of course," Mycroft agreed. He gave what was probably supposed to be a reassuring smile, but his face just wasn't designed for it. "I am disinclined to think that Britain is quite so defenseless as certain parties would have us believe. James Moriarty and I are not the only people who prefer to work from the shadows."

"Right," said John, who had no idea what that meant and didn't particularly care. "But you will be able to turn Sherlock back?"

"Undoubtedly," said Mycroft. "With time."

"With time," John repeated. He looked down at the not-rodent in his arms. It had fallen asleep. "I suppose I'll need some food for you, then."


	3. Chapter 3

Thankfully, Molly Hooper was available to ferret-sit at eight o'clock on a Friday evening. John felt bad for taking advantage of the poor girl, but Mrs. Hudson seemed liable to faint if she was faced with the reality of the situation and he couldn't think of anyone else to call.

"I'm really sorry about this," he apologized as he showed her in.

"Oh, no, it's no problem," she assured him. "It's kind of nice to have something to do, really. Oh, hello!" She lit up at the sight of the ferret, which had slithered out from behind the skull to sniff at her. "What's his name?" she asked, reaching for it.

"He hasn't got one. Careful, he . . ." John watched in amazement as the creature scampered eagerly up Molly's arm and onto her shoulders, making happy little noises. ". . . bites. Blimey."

"Animals like me," she said, with a slightly apologetic smile. "More than humans do, really. Maybe they think I smell like food, because I work in the morgue – I mean, no, sorry."

"It's fine, Molly," John sighed. "Thanks for doing this. I won't be long; I just need to pop down to the shops . . ."

"Take as long as you need," she said obligingly. "You should call him Sherlock," she added as he turned to go.

"What?" he questioned, glancing back.

"Nothing, it's silly; it's just . . ." She was blushing. Sherlock really had done a number on the girl. Even when he was ferret, nibbling on her hoodie, he still managed to embarrass her. ". . . he kind of looks like him. That's stupid, sorry . . ."

"No, you're right. That's a good name."

Molly beamed, and John managed a half-hearted smile before he ducked out the door.

A quick internet search had told him that ferrets were carnivores, and that he could get food for them at most pet stores. It had also told him that they slept around seventeen hours a day, but he didn't put much faith in that, seeing as humans were supposed to sleep around eight hours a day and Sherlock generally subsisted on less than half of that. It took him a little more than an hour to find a pet store, fend off the vendor who was trying to sell him a large selection of over-priced ferret merchandise, and get back to 221b.

"Sorry it took me so long," he said as he elbowed the door open. "It is frankly ridiculous the amounts of money people are apparently willing to spend on their pets . . ."

He trailed off as he turned around to see Molly making fluttery shushing motions from where she was perched on the couch. He frowned at her questioningly, and she gestured behind her. Confused, he moved forward – and stopped in his tracks, his eyes widening. There, curled in Molly's hood as if it were a hammock, was the ferret. _Sherlock_ the ferret.

Said ferret was making tiny mewling noises in his sleep.

"Uh . . . right," he said, quietly. "We probably don't want to wake him. I mean, if you don't mind staying for a bit. I'll just . . . make us some tea."

Molly was still sitting very still when he returned with the tea, a small, thoughtful frown on her face.

"Thank you," she said, accepting the tea. "Do you . . ."

He gave her an encouraging nod when she paused.

"Do you know where he came from?" she asked.

John gave an intentionally vague shrug.

"He just kind of appeared," he said, truthfully enough. "Sherlock has a hand in it, no doubt. He's been out."

Carefully, so as not to disrupt her slumbering passenger, Molly nodded, biting her lip.

"The thing is . . . he's so used to people. And – I know you don't have a litter box, but I put some newspaper down – I hope you don't mind –"

"No, no, it's fine," said John quickly. "It's good. I probably should have thought of it earlier."

"Okay, except he seems to know what it's for and everything. Like he's trained. I think . . . I think maybe he's someone's pet."

"I really don't know, Molly," John sighed tiredly.

"No, of course not. Sorry." She dropped her gaze to her teacup, flushing with embarrassment again. "It's only . . . whoever he belongs to, they must miss him."

"Yeah," John agreed, his eyes drifting to where Sherlock's violin sat propped against his desk. "They must."


	4. Chapter 4

The creak of the door as Molly departed was accompanied by a whisper of air from behind John. He turned, and was not at all surprised to find Loki once again lounging in Sherlock's chair. The god reached towards the ferret which had clambered its way onto the desk, but pulled back with inhuman speed when it snapped at him.

"Spirited, isn't he?" Loki commented, false amiability over a constant, unspoken threat. "I expect he's even more . . . stimulating in human form. It's a pity you'll have only memories for comparison."

"Why are you doing this?" John demanded.

"Why not?" Loki replied, spreading his hands in what should have been a careless gesture, but was in reality as meticulously controlled as all his other movements.

"He's no threat to you," said John, clenching his hands on the back of his chair and struggling to remain calm. He had pretended to believe Mycroft's reassurances, but he knew in some sick place deep in his stomach that they had been lies. There was no way to turn Sherlock back. Not now, maybe not ever. He had to go the source. "He's a genius, but all he cares about is the work, and that's strictly Earthbound."

"I am aware," said Loki, looking slightly amused.

"Then what?" John burst out. "What could you possibly want from us? Souls? Contracts signed in blood? First-born children?"

Loki frowned, genuine confusion flashing across his face.

"What use would I have for your spawn?"

"That's not –" John groaned. "Oh, Christ." He bit back his anger, stepped forward, and tried a different tactic. "Look, what he said to you was horrible. Most of what comes out of Sherlock's mouth is a bit horrible. _Sherlock_'s a bit horrible. But I honestly don't think he understands what he's doing."

Loki's brow furrowed.

"He's mentally deficient?"

"No!" said John quickly. He gave a small, weary laugh. "No. He's . . . mentally excessive, if anything. It's emotionally that he's got a problem."

"And yet you care for him anyway?" Loki questioned. "Enough to be his advocate; enough to bargain with me for his well-being, despite knowing my power and what harm I could inflict upon you should I choose?"

"Yeah," John sighed. "Apparently."

"But _why_?" the god demanded, suddenly on his feet and much too close. His arms were braced against the mantle one either side of John, boxing him in, but it was his gaze which really held him pinned. "You are a soldier, and a healer. You are strong and brave and compassionate. You are everything your people value, while he is everything they despise. Why would you care for a man who is so entirely your opposite?"

John held very, very still. He could feel Loki's hot, ragged breaths on his face, could see the desperation in that too-thin frame, and knew that one way or another, he would not get another chance at this.

"Because he's brilliant. And he's not half as horrible as he likes to think he is. And . . . because nobody deserves to be alone. Not even arrogant bastards like him."

Loki stared at him for a long, long moment. Green-blue-grey eyes shimmered with unshed tears, searching, searching, searching . . . and then he was gone.

Sherlock gave a strangled curse as he toppled from the desk.


	5. Chapter 5

**Notes: Last chapter! Thank you so much to everyone who reviewed/favorite/etc. Your feedback and encouragement mean a lot to me. Sorry if this isn't quite the epic revelation some of you were waiting for, but despite my inability to write anything angst-free, I never really intended this to be more than a fluffy crackfic. (Also, Loki is cray-cray.)**

"Wha – Sherlock! You okay?" John questioned, rushing forward to help the consulting detective to his feet. He had never been more relieved to be glared at.

"Yes, yes, I'm fine," Sherlock snapped irritably, straightening his jacket. He paused suddenly, his frown deepening. "Did I bite Mycroft?"

"You remember that?" John asked, a little breathlessly, sinking into his chair.

"Vaguely."

"Yes. Yes, you did." The giddy relief was ebbing, anger simmering to the surface. The worry which he had been attempting to suppress for the past day only enhanced it.

"Oh." Sherlock seemed to consider this for a moment. "Good."

"No, Sherlock," said John, with as much patience as he could muster, which wasn't much. "Not good. Nothing about this whole thing was good. It was, in fact, very, very bad."

Sherlock frowned at him again, and this time the annoyance was mixed with confusion. John sighed in exasperation.

"Look, just, the next time you have a chat with a Norse god, do me a favor and try _not_ to piss him off."

"I only stated the facts," said Sherlock, dropping into his chair. "It's not as if I told him anything he wasn't already aware of."

"He was crying," said John flatly. "General rule of thumb: when the person you're talking to is visibly weeping, that's a hint for you to _shut up._"

"I'll keep that in mind," said Sherlock and god, now he was looking offended. He'd be insufferable for days. John was too tired for this. He rubbed his forehead, feeling a headache coming on.

"John?"

"Christ –" John jumped terribly. Sherlock was directly in front of him, hands gripping the arms of his chair, silver-blue eyes inches from his own.

"John, what did you promise him?"

"What?" he asked, thrown by the sudden urgency in Sherlock's voice.

"Loki! What did you promise Loki to get him to undo the transformation?"

"I – nothing. Are you sure you're okay?"

"Don't try to protect me!" Sherlock growled, surging to his feet. He began to pace, breathing hard, his hands twitching restlessly as if he was barely preventing himself from seizing his own hair – or someone's neck. "He's the Trickster, but it's possible to beat him at his own game. I can get his files; learn as much as possible. Whatever deal you made, we will get you out of it."

"Sherlock –" John stopped, taking a second look at his flatmate. His eyes held the fierce determination which usually made an appearance when he was on a particularly difficult case, but it was coupled with an earnest sincerity which John had only seen a few times. John felt the last of his anger draining away. "Sherlock," he repeated, more gently. "It's okay. Really. I didn't make any sort of deal with him. We only talked."

"You _talked_," Sherlock repeated, as if he had said that they went go-go dancing. "You _talked_ with Loki of Asgard, and he willingly restored me to human form."

"Looks like it, yeah," John answered.

"_Why?_"

"I don't know. He's mad, Sherlock. He is genuinely off his rocker. Out of touch with reality; the lights are on but only because he set the bloody house on fire. Who knows why he does anything?"

Sherlock mulled over the statement. Then, incredibly, he nodded.

"Yes. Yes, of course. The truly insane cannot be held to the normal standards of logical behavior."

". . . . Exactly," said John, slightly startled by the concession but not about to question it. "Good. Glad we agree." He pushed himself to his feet with a groan. "I'm going to bed. Don't – just –"

Sherlock stared at him uncomprehendingly, and he sighed. It was no use to ask that the violin remain silent for the night. Sherlock would only delete or, more likely, ignore the request.

"Never mind. Goodnight." He turned away, moving towards the stairs.

"John."

He turned back. Sherlock was watching him, wearing an oddly vulnerable expression which looked out of place on his sharp features.

"Thank you."

John smiled.

"You're welcome, Sherlock."

~Fin~


End file.
